In a study published today scientists put the panda taste receptors to the test, to uncover whether they would notice the difference between plain water and the sweet stuff.

"Generally speaking, animals that eat plants have a sweet taste receptor because that enables them to detect in plants sugars that are sources of calories," says Professor Gary Beauchamp, director of the Monell Centre that carried out the research.

But pandas stick to one plant - bamboo - which is notoriously low on sugar.

So the researchers wondered whether like many carnivorous animals, including cats, pandas had lost their ability to detect sweetness.

Choice of bowls

When given two bowls of liquid, one sweetened and one not, the eight pandas universally slurped down the sugary brew.

The researchers tested a variety of sugars, including fructose, glucose, sucrose, lactose, maltose, and galactose.

In all cases, the sweet drink was preferred, and especially the ones with fructose and sucrose, which humans perceive as the sweetest.

The scientists also used cellular analysis to show how pandas responded to sugars at a DNA level.

Using DNA collected from the giant pandas during routine health examinations, genes that code for the panda sweet taste receptor were isolated and then inserted into human host cells grown in culture.

These cells responded vigorously to sugars but not to most artificial sweeteners.

This step helped investigators confirm pandas have a functional sweet taste receptor that underlies their ability to detect and respond to sugars.

The researchers speculate pandas may hold on to working sweet receptor cells because, beyond the taste factor, they may be used in places like the pancreas and the gut to help with plant digestion.

"This is the first study to address taste perception in the giant panda as it relates to feeding behaviour," says lead author Dr Peihua Jiang, a molecular biologist at Monell.

"We hope to extend this research further to examine bitter taste perception. The results could have significant implications for the conservation of this endangered species as their natural habitats continue to be demolished."

Why bamboo

But if pandas love sweets, why do they only eat bamboo?

In captivity, pandas do enjoy sweet foods - including Washington's newest panda cub Bao Bao, who "is apparently relishing sweet potato as a first food during weaning", says Dr Danielle Reed, a co-author on the study.

But pandas also need lots of bamboo, or they get sick. One hypothesis is that the reedy plant provides something necessary, so evolutionary pressure has led them to rely solely on the plant.

Another possibility being tested, Beauchamp says, is that for pandas, bamboo actually tastes like candy.

After all, there is definite evidence different animals experience foods differently.

Examining an animal's taste DNA can give us clues to their past diet, knowledge that is particularly important for endangered animals in captivity, says Reed.

"This process can provide information on approaches to keep such animals healthy," she says.